Porous materials have a host of uses. Common uses for leather and porous polyurethane are to produce clothing and furniture. Common uses for wood include use as a building material and for the production of furniture. Polyimide compositions are known to have unique performance characteristics, which make them suitable for uses in the form of bushings, seals, electrical insulators, compressor vanes, brake linings, and others as described in U.S. Pat. No. 5,789,523. Para-oriented aromatic polyamides (para-aramids) are used to make fiber substrates that are useful for wear resistant application.
All of the porous materials described may degrade and decay over time by staining, wetting, warping, tearing or wearing. It is desirable to treat porous materials to improve resistance to wear, tear, creep, decay, and degradation by wetting, staining and warping, and to improve durability while maintaining the appearance of the materials.
For many years, textiles have been chemically treated to improve water and oil repellency. Different applications are commercially available to protect different kinds of substrates from oil and water staining. For example, Scotchgard.RTM. brand protector for fabrics sold by the 3M Company, and Teflon.RTM. Fabric Protector sold by E. I. du Pont de Nemours and Company, are available to consumers for use with textiles and fabrics. The use of granular fluoro-compounds is also discussed in Japanese Patent 05318413. The invention involves a method whereby a raw wood material is impregnated with a fluorinated microparticles having a diameter of 5 microns and a compound which changes to insoluble cured resin.
Other references include the treatment of microporous materials with fluoroacrylate to achieve permanent water and oil repellency. For example, U.S. Pat. No. 5,156,780 teaches a method for treating microporous substrates to achieve water and oil repellency while maintaining porosity. In the '780 method, the substrates are impregnated with a solution of monomer in a carrier solvent. The carrier solvent is first substantially removed from the substrate for the express purpose of leaving the monomer as a thin conformal coating on all internal and external substrate surfaces. In this manner, the monomer is converted to polymer and the polymer does not block the pores or restrict flow in subsequent use as a filtration membrane.
If enough fluoromonomer is polymerized into a porous structure, a point is reached at which there is more fluoropolymer than substrate and the composition can be considered a filled fluoropolymer. Fluoropolymers such as PTFE are commonly filled with substances such as glass fibers, graphite, asbestos, and powdered metals (Kirk-Othmer Encyclopedia of Chemical Technology, Fourth Edition, Volume 11, John Wiley and Sons, New York, pages 626 and 630). The filler is generally added for the purpose of improving some property of the fluoropolymer, such as creep or hardness.
Most often, filled fluoropolymers are made by physically mixing the fluoropolymer with the filler or by coagulating an aqueous fluoropolymer emulsion on the filler, but such methods have their problems. Adhesion of fluoropolymer to filler can be quite poor, particularly if the fluoropolymer does not wet the filler and penetrate its pores and finer surface features. Fluoropolymer melts can be very stiff making mixing/dispersion poor and nonuniform. Mechanical mixing can degrade some fillers, for example by breaking fine fibers. It is desirable to polymerize fluoromonomer onto the surface and into the pores of a substrate to achieve intimate fluoropolymer/substrate interpenetration and dispersion with minimal mechanical stress.